Developmental distribution of the glutamate receptor subunits KA2, GluR6/7, and delta 1/2 in the rat medial nucleus of the trapezoid body. A quantitative image analysis.

The medial nucleus of the trapezoid body (MNTB) acts as a relay nucleus in the transmission of auditory information from the cochlear nucleus (CN) to the lateral superior olive. Glutamate receptors mediate the excitatory synaptic transmission in the CN-MNTB projection. Here, we used immunohistochemistry to investigate the expression pattern of the kainate receptor subunits KA2 and GluR6/7 and the orphan glutamate receptor subunits delta 1/2 in principal neurons of the rat MNTB during early postnatal development (P2-59). To objectively quantify the intensity of immunoreactivity, images were scanned with a CCD camera and used for gray-value measurements. At all ages analyzed, each of the three antisera produced immunoreactivity in the somata of MNTB principal cells and in the neuropil. KA2 immunoreactivity of somata and neuropil remained nearly constant between P2 and 23. In contrast, the intensity of GluR6/7 immunoreactivity of somata and neuropil increased between P2 and 6, followed by a decrease until P10. Between P10 and 23, GluR6/7 immunoreactivity of neuropil remained nearly constant, whereas it increased in the somata. In both somata and neuropil, the intensity of delta 1/2 immunoreactivity decreased between P2 and 10, reaching a constant, low level by P10. Our results demonstrate the continuous presence of the glutamate receptor subunits KA2, GluR6/7 and delta 1/2 in the developing MNTB, yet quantitative changes occur which may be associated with functional differences.